MCP Verification Gate: check an MCP server or an A2A agent before you connect or delegate

🛡️ HORIZON SHIELD

Verifiable construction estimate auditing for AI agents

Don't trust the estimate. Verify it.

An MCP server that lets AI agents check whether a Japanese construction or renovation estimate is fair, against open data, and returns a result anyone can verify against Bitcoin (OpenTimestamps). No account, no key.

NENRIN: tree rings for AI facing services

A tree adds one ring a year. Nobody can paint one in afterwards. NENRIN gives that property to software services.

In one thirty day window, measured 2026-08-17, this server appeared in 93,983 AI search results. How many of those became a call from outside, we cannot say. The usage counter deliberately stores no IP addresses, so it cannot separate our own automated checks from external traffic. An earlier version of this paragraph said the answer was 0. This instrument cannot establish that, so the claim is withdrawn here rather than quietly deleted. Discovery is solved. Choice is not. An agent picking between 90,000 servers can only read what each vendor wrote about itself. NENRIN adds the missing layer: records of conduct that the vendor did not author and cannot delete.

How it works, in three lines:

1. Open witnessing. Anyone can measure any endpoint and submit the walk to the public ledger under their own name and vantage. The operator holds no veto: acceptance is mechanical schema checking, and the code that enforces this is in this repository.
2. Discrepancies are the product. When two witnesses report incompatible observations of the same target, the disagreement itself becomes a permanent, citable record. The founding one is real: NENRINDISCREPANCY0001, two honest witnesses, one target, both correct.
3. Rings. Each month the accepted records bundle into a ring that carries the hash of the previous ring, timestamped to Bitcoin. Eighteen months of rings cannot be created in an afternoon, by anyone, including us.

The specification is anchored on the public ledger as entry 19 (sha256 9ccba2e325fd2a555fcdb2dec519b8c6bf7a669064674846aea98ecfff824e3d): NENRINSPECv1.md. It names its own prior art (Certificate Transparency, Rekor, in-toto, SLSA, OpenTimestamps), states exactly which combination is claimed as new, and invites refutation into the same ledger.

The witness intake is live. Start here:

curl -s https://ledger.horizonshield.dev/witness

We are the first test subject under our own rules. The ledger keeps the record of our gate failing its own test, and the full 522 incident that started all of this. Unflattering records stay.

Shortened. The full README is on GitHub.